Well, 4f is an electron from a 4f electron, but I guess you knew that part, already, right?

The indices 7/2 and 5/2 indicate that the electrons exhibit coupled states thus resulting in a split signal. For any angular momentum or spin phenomenon multiplicities of coupled states are calculated by 2J+1, that means you should observe two 4f signals whose intensities should have the ratios:

7/2*2+1=8

5/2*2+1=6

->8/6=4/3=I(4f7/2)/I(4f(5/2)

In reality you will observe slight deviations from that because the cross sections for the photoemission are not fully identical. Therefore, if you evaluate your XPS in order to calculate a stoichiometry, check out whether your software is using a set of cross sections that includes coupling or one that doesn't.

The most popular sets are probably the Scofield and the Yeh sets; Scofield includes this effect while Yeh doesn't; on the other hand, Yeh used a slightly better calculation method, so for the choice of the set I would set the preference like this:

-you don't use peaks with coupled signals (as in most of my own XPS work) -> Yeh

-your evaluation requires the interpretation of coupled signals ->Scofield

Dear Farooq Adil Syed,

This is due to spin-orbit splitting.

First we must remember the quantum numbers:

n: main quantum number

l: angular momentum quantum number

ml: magnetic quantum number

s: spin quantum number

At this point we will focus on l and s.

l = 0, 1, 2, 3 (s, p, d, f)

s = 1/2, -1/2.

And finally we have j: total angular momentum.

j = l ± s.

So for example in your case a 4f orbital

l = 3, then j = 3 + 1/2 and j = 3 - 1/2

j = 7/2 and j = 5/2.

Orbital l j Area ratio (2j + 1)

s 0 1/2 -

p 1 3/2, 1/2 4:2 (2:1)

d 2 5/2, 3/2 6:4 (3:2)

f 3 7/2, 5/2 8:6 (4:3)

Just saying that one is spin up and one down is wrongly overfacilitating; those coupled states are degenerate and each involves a number of energetically equivalent states (that's where the multiplicity comes from). You will only be able to differentiate between "up" and "down" cases if you apply a Zeeman or Stark effect scenario which is not the case in usual XPS.